However, while the dielectric constant of tantalum oxide is increased when the oxide is crystallized, the annealing treatment for crystallizing tantalum oxide is accompanied by a problem of oxidation of the lower electrode of the capacitor.
More specifically, the tantalum oxide formed by a vapor-phase deposition method such as CVD is in an amorphous state and, if it is subjected to an annealing treatment for crystallization at a temperature higher than about 700xc2x0 C., it releases some oxygen contained therein. As a result, the tantalum oxide becomes deficient of oxygen to consequently reduce its insulating effect and, at the same time, the lower electrode is oxidized by the oxygen that is released from the tantalum oxide. In the case where the lower electrode is formed of polysilicon, silicon oxide (SiO2) is produced by the oxidation to compensate for the crystal defects of the tantalum oxide to some extent and suppress reduction in the insulating effect, although the capacitance of the capacitor is inevitably lowered. On the other hand, where the lower electrode is formed of a metallic material, electric leakage can easily occur because no high quality metal oxide is uniformly produced unlike the case of using polysilicon for the lower electrode.
Therefore, it is an object of the present invention to provide a method of manufacturing a capacitor that can suppress the oxidation of the lower electrode and, at the same time, improve the quality of the tantalum oxide film.
As a result of a series of intensive research efforts for achieving the above object, the inventors of the present invention have found that the oxidation of the lower electrode can be minimized and the density of the tantalum oxide can be increased to improve the capacity of the capacitor and prevent electric leakage from taking place, by compensating for the oxygen deficiency of the tantalum oxide by means of a treatment with active oxygen species and conducting the annealing at a temperature lower than the crystallization temperature of tantalum oxide by 10xc2x0 C. to 80xc2x0 C. The present invention is based on these findings.
According to a first aspect of the present invention, there is provided a method of manufacturing a capacitor having a tantalum oxide film as insulating film, the method comprising: vapor-phase depositing a tantalum oxide film on a lower conductive film; treating the tantalum oxide film with active oxygen species; annealing the tantalum oxide film treated with the active oxygen species, at a temperature lower than the crystallization temperature of tantalum oxide by 10xc2x0 C. to 80xc2x0 C. in an inert atmosphere; and forming an upper conductive film on the annealed tantalum oxide film.
According to a second aspect of the invention, there is provided a method of manufacturing a capacitor having a tantalum oxide film as insulating film, the method comprising vapor-phase depositing a tantalum oxide film on a lower conductive film; annealing the tantalum oxide film at a temperature lower than the crystallization temperature of tantalum oxide by 10xc2x0 C. to 80xc2x0 C. in an inert atmosphere; treating the annealed tantalum oxide film with active oxygen species; and forming an upper conductive film on the tantalum oxide film treated with the active oxygen species.
In the first and second aspects of the present invention, the annealing step is preferably conducted at a temperature of from about 620xc2x0 C. to about 690xc2x0 C.
According to a-third aspect of the invention, there is provided a method of manufacturing a capacitor having a tantalum oxide film as insulating film, the method comprising: a first vapor-phase deposition step of vapor-phase depositing a first tantalum oxide film on a lower conductive film; a first annealing step of annealing the first tantalum oxide film at a temperature lower than the crystallization temperature of tantalum oxide by 10xc2x0 C. to 80xc2x0 C. in an inert atmosphere; a first treatment step of treating the annealed first tantalum oxide film with active oxygen species; a second vapor-phase deposition step of vapor-phase depositing a second tantalum oxide film on the first tantalum oxide film treated with active oxygen species; a second treatment step of treating the second tantalum oxide film with active oxygen species; a second annealing step of annealing the second tantalum oxide film treated with the active oxygen species, within a temperature range between a temperature lower than the crystallization temperature of tantalum oxide by 10xc2x0 C. to 80xc2x0 C. and a temperature at which the tantalum oxide crystallizes, in an inert atmosphere; and a step of forming an upper conductive film on the annealed second tantalum oxide film;
wherein the step of forming the second tantalum oxide film, the subsequent second treatment step with active oxygen species and the second annealing step are conducted sequentially at least once, before the formation of the upper conductive film.
Preferably, the first annealing step is conducted at a temperature between about 620xc2x0 C. and about 690xc2x0 C. and the second annealing step is conducted at a temperature between about 650xc2x0 C. and about 750xc2x0 C.
In the invention, the lower electrically conductive film may be formed of a metal-based electrically conductive material such as ruthenium, tungsten, aluminium, platinum, tungsten nitride, titanium nitride, or titanium silicon nitride.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.